BIOLOGICAL VARIATIONS OF BACTERIA 405 



the first place, a somewhat selective action on the different 

 strains of B. coli, and secondly, permitting an immediate re- 

 turn to normal proteolytic activity, under the conditions of 

 experimentation here outlined. 



Aside from the peculiar manner in which B. coli nos. 1 and 2 

 and the cholera spirillum acted on reversion in contrast to the 

 other strains, there is another observation worthy of mention. 

 It was noted that frequently in doing the Salkowski test with 

 these colon strains, a positive reaction occurred without the 

 addition of nitrite. This is rarely found with the B. coli and had 

 not been noticed in any of the control cultures nor m the previous 

 experiments. This pecuharity of the test was quite irregular 

 in its occurrence, it appeared as if at will, and disappeared 

 and re-appeared without any apparent reason, since the con- 

 ditions of the experiment were unaltered. The reverse was 

 often noted with the cholera spirillum, in which case, instead 

 of obtainmg a positive mdol test on the addition of acid alone, 

 none occurred until nitrite was added. This observation would 

 indicate some changes in the power of nitrite formation entirely 

 independent of that of indol production, and would well fit 

 in with the carbohydrate effect upon the other biological activi- 

 ties already mentioned. 



In order further to ascertain the action of the various sugars 

 on the biological activities of the different strains of bacteria 

 in question, a proteid-free medium was used as a base, to which 

 3 per cent of the different sugars was added. Those used were 

 glucose, lactose, saccharose, maltose, and dextrin. Inocula- 

 tions were made from the same stock cultures of B. coli as in 

 the above experiments, a control of each strain being carried 

 in the proteid-free medium itself. The medium selected was 

 the writer's modification of Naegeli's proteid-free medium and 

 had the following composition: 



Ammonium tartrate ^ 



Potassium phosphate 



Magnesium sulphate 



Calcium chloride ^ 



Glycerin ^^-^ 



Water ' 1000 



